Device for achieving uniform distribution of airborne fibres, e.g. cellulose-fibres

ABSTRACT

A device for achieving uniform distribution of airborne fibres, for instance cellulose-fibres, in the outlet of a conduit intended for the air-transport of fibres, the device being placed in the outlet (10) of the conduit. In accordance with the invention, the device includes a plurality of mutually similar, concentrically arranged circular rotors (1) and a plurality of semi-circular stators (6) which are disposed between the rotors on the outlet side of the device.

The present invention relates to a device for achieving uniformdistribution of airborne fibres, for instance cellulose-fibres, in theoutlet of a conduit intended for the transportation of airborne fibres,said device being placed in said outlet.

In the manufacture of absorption bodies, it is normal practice to suckairborne cellulose-fibres into a vacuum mould provided with anair-permeable bottom, with the aid of subpressure, in a manner such asto fill the mould and to ensure that the fibres are held therein. Theabsorption body formed in the mould is, at present time, subjected tofurther treatment, such as to compaction for instance, in order toimprove its properties. It is also known to produce absorption bodieswhich consist of two sub-bodies of mutually different densities, so asto improve the total absorption and liquid-dispersing properties of theabsorbent body.

With this in mind, it will be understood that progressively higherdemands are placed on the homogenity of the absorption bodies produced,and that local variations in density, for instance due to agglomerationof the airborne fibres introduced into a mould, cannot be tolerated tothe same extent as was previously the case.

Consequently, in order to produce homogenous absorption bodies it isessential that the airborne fibres supplied to a vacuum mould aredistributed uniformly in the air flow carrying said fibres.Unfortunately, this is not achieved in the case of present dayair-transportation conduits, in which fibre-agglomerates, reaching thesize of table-tennis balls in some instances, are formed to varyingdegrees, depending on the lengths of the conduits concerned and themanner in which the conduits are laid and positioned, the moisturecontent, etc.

The object of the present invention is to solve the above-mentionedproblem by mounting in the outlet of an air-transportation conduit adevice which is operative to break-up any agglomerates which may formand to ensure that the airborne fibres will be uniformly distributedwhen exiting from the conduit.

To this end, there is provided, in accordance with the invention, adevice which comprises a plurality of mutually similar andconcentrically arranged circular rotors and a plurality of semi-circularstators, which are disposed between the rotors on the outlet side of thedevice. Because the through-flow area on the outlet side of the deviceis reduced drastically by the presence of the rotors and stators, thevelocity of the air flow will be increased markedly during its passagethrough the device-outlet. This increase in velocity, together with therotary motion of the rotors, will produce turbulence in the air flowwithin the device, this turbulence either being effective todisintegrate fibre-agglomerates directly or in causing the fibres ofhigher velocity to strike against the rotor or stator walls.

An exemplifying embodiment of the invention will now be described withreference to the accompanying drawings, of which

FIG. 1 shows a rotor forming part of the inventive device, from above;

FIG. 2 is a cross-sectional view taken on the line II--II in FIG. 1;

FIG. 3 shows a stator forming part of the inventive device from above;

FIG. 4 is a sectional view of a device constructed in accordance withthe invention; and

FIG. 5 is a part view seen in a direction from the outlet side of theinventive device towards the inlet side thereof.

FIGS. 1 and 2 illustrate a circular rotor 1 which forms part of theinventive device. The mutually opposing surfaces of the rotor peripheryhave provided thereon turbulence-generating elements, which in the caseof the illustrated and described embodiment have the form of ribs 2which extend from the rim of the rotor in towards the centre thereof.The radial extension of the ribs is suitably equal to one-quarter of theradius. The mutually opposing surfaces of the rotor are also providedwith stiffening ribs 3, which extend radially from the rotor hub 4 to alocation level with the inward extremity of the turbulence-generatingribs 2.

FIG. 3 illustrates a stator 6 which forms part of the inventive deviceand which is semi-circular in shape. The stator 6 also has radiallyextending ribs provided on the periphery thereof, these ribs beingreferenced 7 and having the same form as the turbulence-generating ribs2 on the rotor 1. Arranged at either end of the stator is a respectiveattachment means 8 which, in the illustrated case, enable the stator tobe clamped firmly to vertical rods.

FIG. 4 is a sectional view of an inventive device comprising rotors 1and stators 6 located between the ribs. The spacing between the ribs 2and 7 of the rotors and stators respectively is preferably 2 mm. Therotors are mounted on a shaft 9 by means of some suitable connectingmeans, for example by means of a key or spline connection. The shaft 9is driven for rotation by means of a drive (not shown), for instance abelt transmission connected to the output shaft of an electric motor.The rotors may be rotated at a speed of from 3000 to 5500 rpm.

As beforementioned, the inlet side of the device is connected to theoutlet 10 of a conduit intended for transporting airborne fibres, andthe outlet side of the device is connected to the inlet of afibre-delivery chamber from which airborne fibres are sucked into vacuummoulds.

FIG. 5 is a part view illustrating that the sequentially stacked stators6 form side-wall sections of the inventive device. These side-wallsections are provided with grooves or channels 10', as illustrated inFIGS. 3 and 5.

The device operates in the following manner.

As the result of pressure difference, the air will flow from thetransport conduit outlet 10 through the device and into the inlet 11 ofthe fibre-delivery chamber. Because the through-flow area of the deviceon the outlet side thereof is much smaller than on the inlet side ofsaid device, due to the presence of the rotors 1 and stators 6, thevelocity of the air will increase markedly in the region of thestationary stators 6. As the rotors rotate at high speed, powerfulturbulence is created in this region of the device. This turbulence iseffective to disintegrate any fibre agglomerates present in theair/fibre mixture arriving from the transport conduit, suchdisintegration being effected directly, or indirectly by high-velocityimpact of the fibre agglomerates against the walls of the rotors orstators. The rotational movement of the rotors will also impart to thefibres a velocity component acting in the direction of rotor rotation,and consequently the fibres will be uniformly distributed peripherallyupon their exit from the device. Uniform distribution of the fibres inan axial direction is achieved by the local air-vortices created on theoutlet side of the device immediately externally of the periphery of therapidly rotating rotors.

The width of the gap between stators and rotors will naturally beselected primarily in dependence on the dimensions of the fibres. It hasbeen found experimentally that a gap of 2 mm provides good results inthe case of cellulose fibres. Although narrower gaps are conceivable,the devices then required for handling the air/fibre mixture flowingthrough the transportation conduit at a speed of 20-30 m/sec become muchtoo bulky and unmanageable, due to the fact that the through-flowcapacity of the inventive device is then relatively small. Gap widths ofup to 3 mm will also provide acceptable values of fibre distribution inthe air exiting from the device.

As will be understood, the inventive device can be modified in severalrespects within the scope of the invention. For instance, the shape ofthe rotors and the number of rotors used can be varied, and theturbulence-generating elements may have a form different to thatillustrated. The invention is therefore restricted solely by the scopeof the following claims.

I claim:
 1. A device for achieving uniform distribution of airbornefibres, for instance cellulose-fibres, in the outlet of an air-transportfibre conduit, said device being placed in said outlet (10) and havingan outlet side and an inlet side, characterized in that the deviceincludes a plurality of mutually similar and concentrically arrangedcircular rotors (1), and a plurality of semi-circular stators (6) whichare disposed between the rotors on the outlet side of the device.
 2. Adevice according to claim 1, characterized in that the rotors haveprovided on tips thereof ribs which extend between mutually opposingsurfaces of the rotors.
 3. A device according to claim 1, characterizedin that turbulence-generating elements (2, 7) are provided on mutuallyopposing side-surfaces of the rotors (1) and the stators (6).
 4. Adevice according to claim 3, characterized in that theturbulence-generating elements comprise ribs (2, 7) which extendradially from the periphery of the rotors and the stators in towards thecentres thereof.
 5. A device according to claim 4, characterized in thatthe radial extension of the ribs is approximately equal to one quarterof the radius of said rotors and said stators.
 6. A device according toclaim 5, characterized in that a gap defined between theturbulence-generating elements of the stators and the rotors has a widthof 1 to 3 mm.
 7. A device according to claim 6, characterized in thatthe gap defined between the turbulence-generating elements of saidrotors and said stators has a width of 2 mm.